The problem of operationally monitoring frequency-hopping transmissions has been known since the invention of frequency-hopping radios. A frequency-hopping radio transmits communication data in small signal segments of data, with each typically being at a different frequency to the one preceding and following it. The order and selection of frequencies used within a transmission is selected in accordance with a set of predetermined parameters. Given a same set of parameters as a transmitter, a frequency-hopping receiver, hops frequencies in a near identical fashion to the frequency-hopping transmitter and is thus able to ensure complete and proper reception of the communication data. Thus, by using a predetermined set of parameters for both transmitter and receiver, communication is possible between two radios. This is a very efficient way to reduce signal interference in radio bands where channel assignment is not regulated or where different signal types can be encountered, as in the Industrial, Scientific and Medical (ISM) radio frequency band.
Prior Art receiving radios, used for blind analysis of communication data transmitted using frequency hopping, absent the necessary predetermined set of parameters, hop their receiver frequencies in a different order than the transmitting radio and as such, even if they receive a segment of the transmission, are not capable of reconstructing the complete communication data. Thus, spread spectrum frequency hopping, is a challenge for spectrum monitoring as it prevents a clear representation of time-coherent signal activities, especially if more than one user is present at the same time instant.
Recently, a few approaches that make use of filter banks for estimating some of the critical predetermined set of parameters associated with frequency-hopping transmitters have been proposed. These techniques rely on filter banks and use a time-frequency plane to detect a single signal and then estimate several of its parameters. While they provide some basic concepts for signal extraction for obtaining a portion of transmitted communication data from a single source, they either assume knowledge of key predetermined parameters or assume the presence of only one transmitted signal. Unfortunately, this is unrealistic in an operational environment since typically none of the parameters are known and because many signals are typically transmitted simultaneously in a same local area.
A need therefore exists for a spectrum monitoring and surveillance system for realistic signal environment in spectrum bands in usage today. It is therefore an object of the invention to provide a spectrum monitoring system for monitoring portions of a communication from a frequency hopping radio transmitter that overcomes limitations in the prior art for wireless communication applications.